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Topic: Tautomer

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	tautomer - HighBeam Encyclopedia (Site not responding. Last check: 2007-11-03)
		tautomer, one of two or more structural isomers that exist in equilibrium and are readily converted from one isomeric form to another.
		Of the various types of tautomerism that are possible, two are commonly observed.
		It arises as a result of the aldehyde group (-CHO) in a sugar chain molecule reacting with one of the hydroxy groups (-OH) in the same molecule to give it a cyclic (ring-shaped) form.
	www.encyclopedia.com /doc/1E1-tautomer.html (278 words)

	Get To Know Histidine
		Release of proton from the upper nitrogen of B produces the imidazole tautomer A, and release of proton from the lower nitrogen produces imidazole tautomer C. The tautomers equilibrate by way of the protonated form B. At pH values near 7, all three forms, A, B, and C, are present in equilibrium.
		Because the acid form, imidazolium B, is a hybrid of the two contributors, it is plausible to show release of a proton from either nitrogen atom in proposing a reaction mechanism involving the imidazolium form as a general acid.
		Because the base form, imidazole, exists as two equilibrating tautomers A and C, it is plausible to write either tautomer in proposing a reaction mechanism involving the imidazole form as a general base.
	www.usm.maine.edu /~rhodes/Goodies/Get2NoHistidine.html (561 words)

	Carbonyl Reactivity
		From previous knowledge and experience, we surmise that the common intermediate is an enol tautomer of the carbonyl reactant.
		Clearly, the proportion of enol tautomer present at equilibrium is a critical factor in alpha substitution reactions.
		Although the keto tautomer route is not unreasonable (recall the enhanced acidity of the alpha-hydrogens in carbonyl compounds), the enol tautomer provides a more favorable pathway for both acid and base-catalyzed elimination of the beta oxygen.
	www.cem.msu.edu /~reusch/VirtualText/aldket2.htm (3430 words)

	Inhibition of porphobilinogen synthase (PBG-synthase) by 4,6-dioxoheptanoic acid (1) and related compounds
		The tautomer 1 is analogous to the intermediate (E-iminium ion) obtained by the fixation of the first substrate on the enzyme.
		This tautomer formally results from the release of HO The tautomer 2 is clearly more stable and results from a formal release of water.
		For the tautomer 1 the presence of a carboxylate in the
	www.unine.ch /chim/echet98/107/107_Discus.html (2488 words)

	Ab initio Modeling of the Structural Defect
		This modest improvement is small compared to the absolute energy difference between the tautomers, which is on the order of 80 kJ/mol in favour of the amide isomer.
		The relative molecular energies of the tautomers suggests that a minor stabilization of the imidate form over the amide form does take place when long conjugated chains are associated with the core component.
		Nonetheless, it appears that there might be good communication between the conjugated sidechains through the non-conjugated amide core, and therefore the presence of defects in the real polymers might not be exceedingly detrimental to their electrochemical properties.
	mmrc.caltech.edu /colin/science/past/PhD/html-thesis/node41.html (658 words)

	Forthcoming Paper (Site not responding. Last check: 2007-11-03)
		Tautomer contributions to the near UV spectrum of guanine: towards a refined picture for the spectroscopy of purine molecules
		First, a large variability of the tautomer distribution in the gas phase is found within the purine family, in particular a molecular change, as simple as a 9-methylation on guanine, can reduce the tautomer distribution to a single species (enol form).
		Since the absorption spectrum is tautomer-dependent as well as substituent-dependent, it turns out that the tautomer population is one of the major parameters that control the overall shape of the UV spectrum.
	www.edpsciences.org /articles/epjd/forth/abstracts/chin.html (316 words)

	Chapter 6 - Biologically Interesting Molecules
		The existence of a low-energy tautomer could have far-reaching consequences, given that cytosine is one of the nucleotide bases and its valence structure is key to hydrogen bonding in DNA.
		Note, however, that were the energy of an alternative tautomer only 3 kcal/mol higher than that for the "normal" structure, this would translate into a relative abundance of only about 1% at room temperature.
		Thus, any alternative tautomers would need to be very close in energy to the lowest-energy tautomer to have noticeable effect.
	www.wavefun.com /software/spartan04_win/win_manual/Chapter6_7.html (242 words)

	ANTA. Prop., Explos. and Pyrot. (1994) 32-41. (Site not responding. Last check: 2007-11-03)
		Semiempirical and ab initio structures for 1H, 2H and 4H tautomers of ANTA are gathered in Tables 1 and 2, respectively.
		Amino group is less negatively charged (and nitro group more negatively) for the 4H- tautomer than for 1H- and 2H- ones, being the electronic charge of the ring smaller for 4H- tautomer than for the 2H- and the later one smaller than for the 1H- tautomer at 6-31G* level.
		Then, the insensitivity of ANTA (49a) will be considerably decreased if tautomer 2H- could be present, although this fact is rather difficult because 2H- is termodinamically less stable (1.9 kcal/mole) and, also, its dipole moment is less than a half of the 1H- tautomer one, preventing its presence in polar solvents.
	www.uam.es /departamentos/ciencias/qfa/especifica/depazanta.html (5618 words)

	Daylight Properties Package Reference Manual
		The canonical tautomer is the one generated by using the relative electronegativities of the atom types (O > S > Se > Te > N > C) as graph invariants to preferentially assign double bond and hydrogen positions in the tautomer.
		Although this tautomer often corresponds to the lowest energy form, it is not guaranteed, as it's generated from graph theory and does not consider extended electronic factors.
		Tautomers are computed without using aromaticity and their kekule SMILES are returned.
	www.daylight.com /dayhtml/doc/dayprop (3079 words)

	MN.TAUTOMER: Enumeration of tautomers
		enumerates all possible tautomers but can be restricted to generate only a unique tautomer (one of the most probable)
		TAUTOMER generates either all tautomers of a input structure or only one, but unique tautomeric form.
		The output file consists of altogether 24 tautomers, six of them are shown below.
	www.mol-net.de /software/tautomer/index.html (112 words)

	Properties
		In fact its absorption maximum is found between those of (2) and (3), indicating that (1) is a mixture of the 1,5- and 2,5-di-NH tautomers.
		The X-ray interferogram of (1) shows a hydrogen bridge between the 1-NH group and 7-N of another molecule, while 2-N is bound to the hydrogen of a 5-NH group, suggesting that in the crystal allopurinol is present as the 1,5-di-NH tautomer.
		Likewise in compounds (2) and (3) and all the dimethyl derivatives, the 1,2-disubstituted form is always the least stable, and 1,2-dimethylallopurinol is still unknown.
	www.ch.ic.ac.uk /local/projects/sasithorn/prop.htm (840 words)

	Keto-enol tautomerism - Wikipedia, the free encyclopedia
		A compound containing a carbonyl group (C=O) is normally in rapid equilibrium with an enol tautomer, which contains a pair of double bonded carbon atoms adjacent to an OH (hydroxyl) group, C=C-OH.
		Rare enol tautomers of the bases guanine and thymine can lead to mutation because of their altered base-pairing properties.
		In certain aromatic compounds such as phenols the enol is important due to the aromatic character of the enol but not the keto form.
	en.wikipedia.org /wiki/Keto-enol_tautomerism (748 words)

	Tautomerism - Chemistry (Site not responding. Last check: 2007-11-03)
		Tautomers are structurally distinct isomers in rapid equilibrium (usually).
		2-hydroxy pyridine and 2-pyridone are tautomers and are distinct isomers which can be detected spectroscopically.
		2-hydroxy pyridine is the predominate tautomer in the gas phase.
	chemistry.tidalswan.com /index.php?title=Tautomerism (125 words)

	Exam 1 Answers (Site not responding. Last check: 2007-11-03)
		First, the keto-enol tautomer has the double bonds in conjugation, which is always stabilizing relative to non-conjugate pi-bonds.
		This hydrogen bond stabilizes this tautomer, overcoming the usual favorability of the keto form over the enol.
		The diketo tautomer suffers from dipole-dipole repulsions that forces the carbonyls to be far away.
	www.trinity.edu /sbachrac/chem2320/fall2004/test1Answers.htm (256 words)

	Research
		Presumably because of their low intensity, no signals of the tautomer B could be detected.
		Apart from intense bands attributalble to tautomer A, bathochromically shifted shoulders of low intensity are observed in the low-energy and the high-energy part of the spectrum (Q band region and Soret band region).
		The calculated energy difference between tautomer B and tautomer A of 6.6 kJ/mol (vacuum) agrees reasonably well with the experimental reaction enthalpy of 5.1 kJ/mol which was determined from the temperature dependent measurements using the van't Hoff equation.
	www.uni-koeln.de /math-nat-fak/phchem/hohln/bremm/research.html (536 words)

	W0122: Influence of Intermolecular Forces on Uracil Tautomer Selection (Site not responding. Last check: 2007-11-03)
		The crystal structures of several zinc complexes with uracil are used to illustrate the influence of intermolecular forces on the nature of the coordination compounds formed by this polyfunctional ligand.
		The N1 and N3 tautomers are observed in two separate systems in which the hydrogen bonding patterns in the extended structures favor one or another disposition of uracil.
		N3)(NH the presence of both tautomers in the same complex is confirmed structurally for the first time; and the solid-state hydrogen bonding pattern is clearly implicated in the nature of the product isolated.
	www.hwi.buffalo.edu /ACA/ACA01/abstracts/text/W0122.html (161 words)

	Chem 569
		Identify the more stable tautomer and calculate the energy of the higher-energy tautomer relative to it.
		Although the equilibrium concentration of enol tautomers is typically very small and, because of this, enols are very difficult to isolate and characterize, they are believed to play an important role in the chemistry of carbonyl compounds
		The mechanism of acid catalysis involves protonation at the carbonyl oxygen followed by deprotonation either at the a carbon, leading to the enol tautomer, or at oxygen, leading back to the original keto form.
	www.siue.edu /CHEMISTRY/eilers/projects/final-project.html (1348 words)

	Use of 2-amino-4-heteroarylethyl-thiazoline derivatives as inhibitors of inducible no-synthase - Patent 6872740
		a racemic mixture, an enantiomer, a diastereoisomer or a mixture thereof, a tautomer thereof, or a pharmaceutically acceptable salt thereof.
		a racemic mixture, an enantiomer, a diastereoisomer or a mixture thereof, a tautomer thereof, or a pharmaceutically acceptable salt thereof, in combination with a pharmaceutically acceptable carrier.
		The pharmaceutical compositions according to the invention consist of a compound of formula (I) or an isomer or tautomer or salt of such a compound, in pure form or in the form of a composition in which it is combined with any other pharmaceutically compatible product, which may be inert or physiologically active.
	www.freepatentsonline.com /6872740.html (3415 words)

	Chapter 4 - Groups of Organic Molecules
		2-hydroxypyridine is in equilibrium with its tautomer, 2-pyridone.
		The relative abundance of the two is given by the Boltzmann equation and depends both on their relative energies and on the temperature.
		While this does not establish that the latter is a more stable tautomer, it suggests that this is the case.
	www.wavefun.com /software/spartan04_win/win_manual/Chapter4_28.html (162 words)

	Triazoloquinazoline compounds, and their methods of preparation, pharmaceutical compositions, and uses - Patent 4713383
		The compound of claim 1 wherein R.sub.1 phenyl which is unsubstituted or substituted by fluorine or chlorine in the ortho or meta position; and Ring A is unsubstituted or substituted by chlorine at the 9 position;
		A method counteracting the effects of adenosine and of treating asthma comprising administering to a mammal in need of such administration an effective amount of a compound of claim 10, a tautomer thereof, or a pharmaceutically acceptable salt of said compound or said tautomer.
		A pharmaceutical composition comprising an adenosine antagonistic effective amount of a compound of claim 10, a tautomer thereof, or a pharmaceutically acceptable salt of said compound or tautomer; and a pharmaceutically acceptable carrier.
	www.freepatentsonline.com /4713383.html (10143 words)

	tautomer - OneLook Dictionary Search
		Tip: Click on the first link on a line below to go directly to a page where "tautomer" is defined.
		tautomer : Dorland's Illustrated Medical Dictionary [home, info]
		Tautomer : Drug Discovery and Development [home, info]
	www.onelook.com /?w=tautomer (112 words)

	7-Aminopyrazolopyrimidine (Site not responding. Last check: 2007-11-03)
		Semiempirical MO theory will be used to estimate the tautomeric preferences in this system as a means to probe the inherent relative stabilities of the possible bound tautomers.
		Then, the effects of protonation at various positions will be evaluated at the same level of theory (not counting the presumably important influence of the enzyme!).
		Build the N7-H and N8-H tautomers of 7-NH -PP, preoptimize them with force field methods, and finish with a full AM1 or PM3 optimization.
	www.chem.umass.edu /~nermmw/tautomer2.html (234 words)

	MCB411 (Site not responding. Last check: 2007-11-03)
		Given the millions of bases in the genome of even a single cell, it is INEVITABLE that the tautomers will pop up periodically.
		Since the genetic code IS the binary code of hydrogen bonding, this means that the tautomers intermittently 'masquerade' as other members of the code.
		Shown below are tautomeric forms of the Big 4 (again, tautomerization is a result of interaction with water; that's where the moving Hydrogens go to and come from).
	www.blc.arizona.edu /courses/mcb411b/MoBiByMe/Tautomers.html (419 words)

	Tautomers/Tautomerism
		In part, tautomers are "isomers that are rapidly interconverted." Frequently, however, the less stable of two tautomers is the important on terms of a compound's ability to exhibit a particular sort of chemical reactivity.
		The most important type of tautomerism in organic chemistry are keto-enol tautomers.
		Primarily because of the much greater strength of a carbonyl double bond as compared with an alkene double bond, the keto form is usualy the more stable of the two.
	www.personal.psu.edu /faculty/t/h/the1/tautomer.htm (155 words)

	Internet Electronic Journal of Molecular Design
		We studied interactions of one of the N7 of adenine and its tautomer with alkali metals (Li, Na, Rb and Cs) and alkaline earth metals (Mg, Ca, Sr and Ba) by ab initio calculations.
		The interactions of alkali and alkaline earth metals with N7 of adenine and its tautomer stabilize rare tautomer respect to major form.
		Metalation of N7 of adenine and its tautomer by alkali and earth alkali metals cause to stabilize the rare tautomers.
	www.biochempress.com /av03_0789.html (318 words)

	Online demonstration of the tautomer enumerator MN.TAUTOMER
		If you would like to try our service "Enumeration of Tautomers", please follow these two steps.
		The enumeration of tautomers for up to 50 structures is free of charge.
		We reserve the right to log them and use them to evaluate program performance.
	www.mol-net.com /online_demos/tautomer_demo.html (134 words)

	CiteULike: A xylobiose-derived isofagomine lactam glycosidase inhibitor binds as its amide tautomer. (Site not responding. Last check: 2007-11-03)
		CiteULike: A xylobiose-derived isofagomine lactam glycosidase inhibitor binds as its amide tautomer.
		A xylobiose-derived isofagomine lactam glycosidase inhibitor binds as its amide tautomer.
		The atomic-resolution structure of a xylobiose-derived isofagomine lactam in complex with the xylanase Xyn10A from Streptomyces lividans reveals that the lactam is bound to the enzyme as the amide tautomer, with "reversed" protonation-states for nucleophile and acid-base.
	www.citeulike.org /user/papatonyhill/article/875869 (139 words)

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